How long will it take to transfer my domain to Porkbun?

Max. time for a domain to transfer from one registrar to another:
five days.

Transfers take five days by default, but can complete in as few as 20 minutes in some cases. 

It’s entirely up to your old registrar whether the transfer can occur before five days have elapsed. Some registrars always wait the full five days as a matter of policy, others allow their users to bypass the waiting period. If you're looking to get a domain transferred to Porkbun quickly and there's no apparent way to release it early, your best bet is to contact your old registrar's support department and request an expedited transfer. It can't hurt to ask! (But they may say no.)

The five day maximum is set by ICANN’s rules:

“Failure by the Registrar of Record to respond within five (5) calendar days to a notification from the Registry regarding a transfer request will result in a default “approval” of the transfer.”

source:  https://archive.icann.org/en/transfers/policy-12jul04.htm

Please note that the five days begins from the moment the transfer is officially deemed "pending" and listed as "pending transfer from previous registrar" in the transfers area of Porkbun, not the moment of purchase. Additional delays occasionally occur depending on time zones, registry high jinks, gremlins, etc.